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Use of Previous HitDrillNext Hit-Bit Energy as Downhole Seismic Source

James W. Rector, Bruce P. Marion, Bernard Widrow

A new borehole seismic technique, the Tomex Survey, uses the seismic emanations produced by a Previous HitdrillNext Hit bit during drilling as a downhole energy source. No downhole instrumentation is required for collection of the seismic data, and the data recording does not interfere with the drilling process. The Previous HitdrillNext Hit-bit-generated signals are recorded with sensors attached to the top of the drillstring and at various surface-geophone locations near the well. The sensor output at the top of the drillstring is used as a pilot signal for cross-correlation with the signals recorded at the surface-geophone positions. Cross-correlation is used to determine arrival times and to enhance the signal-to-noise ratio of Previous HitdrillNext Hit-bit-generated events. Deconvolution and time shifts are performed to remov the effects of recording the pilot signal at a location distant from the location of the energy source at the Previous HitdrillNext Hit bit. A direct comparison between data collected using a Previous HitdrillNext Hit-bit source and conventional VSP data shows that the Previous HitdrillNext Hit-bit source yielded comparable data quality.

In using the Previous HitdrillNext Hit bit as a downhole seismic source for inverse VSP, many of the limitations in conventional VSP are overcome. Several applications for VSP that were previously considered by some explorationists to be prohibitively expensive are now feasible. Furthermore, this measure-while-Previous HitdrillTop technique offers the potential for the explorationists to make real-time drilling decisions on site.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.